U.S. patent application number 10/923574 was filed with the patent office on 2005-03-03 for spectrum measuring apparatus and method.
Invention is credited to Ito, Jun, Kanazawa, Hajime.
Application Number | 20050045829 10/923574 |
Document ID | / |
Family ID | 34213770 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050045829 |
Kind Code |
A1 |
Ito, Jun ; et al. |
March 3, 2005 |
Spectrum measuring apparatus and method
Abstract
A spectrum measuring apparatus that includes an extinction
member for decreasing a light intensity from an EUV light source, a
spectrum member for extracting light with a desired wavelength band
from the decreased intensity light and a detector for detecting a
light intensity of the light with a desired wavelength band is
disclosed. Then, a spectrum intensity distribution (spectrum) is
obtained by (a) a plural opening is located in the extinction
member, and the light from the EUV light source passes through the
plural opening at the same time, or (b) the detector detects the
light volume of the light with a desired wavelength band as thermal
energy.
Inventors: |
Ito, Jun; (Tochigi, JP)
; Kanazawa, Hajime; (Tochigi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
34213770 |
Appl. No.: |
10/923574 |
Filed: |
August 20, 2004 |
Current U.S.
Class: |
250/372 |
Current CPC
Class: |
G01J 3/51 20130101; G01J
1/429 20130101; G03F 7/70575 20130101 |
Class at
Publication: |
250/372 |
International
Class: |
G01J 001/42 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 25, 2003 |
JP |
2003-299649 |
Claims
What is claimed is:
1. A spectrum measuring apparatus for measuring a spectrum of a
light that an EUV light source emits, the spectrum measuring
apparatus comprising: an extinction member for decreasing the light
intensity from the EUV light source, a spectrum member for
extracting light with a desired wavelength band from the decreased
intensity light; and a detector for detecting a light intensity of
the light with a desired wavelength band, wherein the extinction
member that has a plural opening, and the light from the EUV light
source passes through the plural opening at the same time.
2. A spectrum measuring apparatus according to claim 1, wherein a
diameter of the plural opening located in the extinction member is
larger than a wavelength of the light that the detector detects the
light intensity.
3. A spectrum measuring apparatus according to claim 1, wherein the
extinction member, the spectrum member and the detector are housed
by a common vacuum vessel, an inner wall of the vacuum vessel has a
reflection coefficient to the light from the EUV light source of
0.1 or less.
4. A spectrum measuring apparatus for measuring a spectrum of a
light that an EUV light source emits, the spectrum measuring
apparatus comprising: an extinction member for decreasing the light
intensity from the EUV light source, a spectrum member for
extracting a light with a desired wavelength band from the
decreased intensity light; and a detector for detecting the light
intensity of the light with a desired wavelength band as thermal
energy.
5. A spectrum measuring apparatus according to claim 4, wherein the
detector is calorie meter.
6. A spectrum measuring apparatus according to claim 4, wherein the
extinction member, the spectrum member and the detector are housed
by a common vacuum vessel, an inner wall of the vacuum vessel has a
reflection coefficient to the light from the EUV light source of
0.1 or less.
7. A spectrum measuring method for measuring a spectrum of a light
that an EUV light source emits, the spectrum measuring method
comprising the steps of: decreasing the light intensity from the
EUV light source via a extinction member that has a plural opening,
extracting a light with a desired wavelength band from the
decreased intensity light; and detecting a light intensity of the
light with a desired wavelength band, wherein in the decreasing
step, the light from the EUV light source passes through the plural
opening at the same time.
8. A spectrum measuring method for measuring a spectrum of a light
that an EUV light source emits, the spectrum measuring method
comprising the steps of: decreasing the light intensity from the
EUV light source, extracting light with a desired wavelength band
from the decreased intensity light; and detecting the light
intensity of the light with a desired wavelength band as thermal
energy.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a spectrum measuring
apparatus that measures spectrum intensity of wide wavelength of a
vacuum ultraviolet region to an infrared region that irradiated
from an EUV light source.
[0002] Conventionally, in photolithography process to manufacture
fine semiconductor devices such as semiconductor memory and logic
circuit, a reduction projection exposure that uses ultraviolet
light is done. The minimum critical dimension transferred by the
projection exposure is proportional to the wavelength of light used
for transfer and inversely proportional to the numerical aperture
("NA") of the projection optical system. Therefore, to transfer the
fine circuit pattern, shorter ultraviolet light wavelengths have
been proposed--from an ultra-high pressure mercury lamp (i-line
with a wavelength of approximately 365 nm) to KrF excimer laser
(with a wavelength of approximately 248 nm) and ArF excimer laser
(with a wavelength of approximately 193 nm).
[0003] However, lithography using ultraviolet light has limitations
when it comes to satisfying the rapidly promoted fine processing of
a semiconductor device. Therefore, a reduction projection optical
system using extreme ultraviolet ("EUV") light with a wavelength of
10 to 15 nm shorter than that of the ultraviolet has been developed
to efficiently transfer very fine circuit patterns of 100 nm or
less. FIG. 11 is a conceptual rendering of the exposure apparatus
that uses the EUV light.
[0004] The EUV light source uses, for example, a light source of
laser plasma (LPP) method or a light source of discharge plasma
(DPP) method.
[0005] The EUV light source of LPP method irradiates a highly
intensified pulse laser beam to a target material put in vacuum,
thus generating high-temperature plasma for use as EUV light with a
wavelength of about 13 nm emitted from this. The target material
may use a metallic thin film, inert gas, and droplets, etc., and is
supplied by a means such as a gas jet in the vacuum. The pulse
laser preferably has high repetitive frequency, e.g., usually
several kHz, for increased average intensity of the emitted EUV
light from the target.
[0006] On the other hand, the EUV light source of DPP method flows
a gas such as Xenon between electrodes, generates the plasma with
the electrical discharge, and generates the EUV light.
[0007] When the EUV light used for the exposure, the EUV light is
absorbed by using a usual metallic mirror and a lens made of quartz
etc. A multilayer mirror that laminates 20 layers with a molybdenum
(Mo) layer and a silicon (Si) layer is used for the EUV light. In
general, the multilayer mirror is adjusted by changing the
thickness of the each layer of the multilayer so that reflectivity
to the EUV light with a wavelength of 13.5 nm is high, and the EUV
light with other wavelengths are absorbed by the mirror.
[0008] An optical system for the EUV exposure apparatus is composed
with several multilayer mirrors. Especially, the EUV light source
of LPP method arranges a condenser mirror surrounding the emission
point to efficiently use the EUV light emitted from the target,
condenses the generated EUV light to a predetermined light
wavelength.
[0009] The light emitted from the target includes not only the EUV
light with the specific wavelength used for the exposure from the
EUV light source of laser plasma method but also the light with a
wavelength band such as the EUV light, X-ray, ultraviolet light,
visible light and infrared light. Thereby, the EUV light with a
wavelength different than the specific wavelength and X-ray light
that can not be reflected by the multilayer mirror are absorbed by
the multilayer mirror, and causes the rise in heat of the mirror.
Moreover, the ultraviolet light activates a residual gas in the
vacuum, and accelerates a deposition of a contamination on the
condenser mirror. The light of the ultraviolet region to the
infrared region is reflected by the multilayer mirror that composes
the optical system of the exposure apparatus, and reaches a wafer.
The light of the ultraviolet region to the infrared region is
absorbed by resist, and heat expands the wafer. As the result,
there is a possibility of decreasing overlay accuracy during
exposure.
[0010] Therefore, it is necessary to measure the wide band spectrum
of the light emitted from the EUV light source, and to measure the
light intensity of the light discharged in each wavelength region
precisely, to design the exposure apparatus that uses the EUV light
and exposure.
[0011] An apparatus that is described to FIG. 12 is disclosed in
Japanese Laid-Open Patent Application No. 2002-175980 (correspond
with U.S. patent Publication No. 2002/085286) about the measurement
of the EUV light emitted from the EUV light source. In FIG. 12, the
EUV light emitted from a condenser point 101 decreases the
intensity of the light by an aperture stop 105, and reflects with a
multilayer mirror 102. Moreover, the EUV light reaches a CCD array
104 through an EUV filter 103 that transmits only an EUV light of a
target for the measurement and is measured.
[0012] Details of spectrum of the EUV light of a predetermined
wavelength region can be measured by a grazing incidence spectrum
system shown in FIG. 13. This method uses the multilayer mirror as
the filter to incidence from a diagonal to two multilayer mirrors
201 and 202. The system can measure the wavelength region of about
5 to 50 nm, and can measure detail spectrum shape because it
adjusts a wavelength resolution (?/?) to 500 or more.
[0013] However, the above-mentioned measuring apparatuses
comparatively measure only a part of the light emitted from the EUV
light source for the wavelength region in the narrow range.
Thereby, it is difficult to measure the entire wide band spectrum
of the light emitted from the EUV light source, and to know the
absolute intensity. As the result, the wavelength intensity
distribution of entire beams including the infrared ray region
emitted from the EUV light source necessary to design the exposure
apparatus that uses the EUV light and exposure stability can not be
obtained.
BRIEF SUMMARY OF THE INVENTION
[0014] Accordingly, it is an exemplary object of the present
invention to provide a spectrum measuring apparatus that can obtain
spectrum intensity distribution of light emitted from an EUV light
source.
[0015] A spectrum measuring apparatus of one aspect of the present
invention includes an extinction member for decreasing the
intensity of the light emitting from an EUV light source, a
spectrum member for selecting a light with a desired wavelength
band from the decreased intensity light and a detector for
detecting a light volume of the light with a desired wavelength
band. Then, it characterizes in (a) a plural opening is located in
the extinction member, and the light from the EUV light source
passes through the plural opening at the same time, or (b) the
detector detects the light volume of the light with a desired
wavelength band as thermal energy.
[0016] Other objects and further features of the present invention
will become readily apparent from the following description of the
preferred embodiments with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a schematic view of a spectrum measuring apparatus
of the first embodiment according to the present invention.
[0018] FIG. 2 is one example of arranging a pinhole array used for
the spectrum measuring apparatus of the first embodiment according
to the present invention.
[0019] FIG. 3 is one example of a pattern of the pinhole array used
for the spectrum measuring apparatus of the first embodiment
according to the present invention.
[0020] FIG. 4 is a schematic view of a state in a measurement
process by the spectrum measuring apparatus of the first embodiment
according to the present invention.
[0021] FIG. 5 is a graph that shown a light absorptance of a
detector used for the spectrum measuring apparatus of the first
embodiment according to the present invention.
[0022] FIG. 6 is a schematic view of a state in a measurement
process by the spectrum measuring apparatus of the first embodiment
according to the present invention.
[0023] FIG. 7 is a schematic view of a state in a measurement
process by the spectrum measuring apparatus of the first embodiment
according to the present invention.
[0024] FIG. 8 is a graph that shown a transmittance of a filter
used for the spectrum measuring apparatus of the first embodiment
according to the present invention.
[0025] FIG. 9 is a schematic view of a spectrum measuring apparatus
of the second embodiment according to the present invention.
[0026] FIG. 10 is a graph that shown a transmittance of a filter
used for the spectrum measuring apparatus of the second embodiment
according to the present invention.
[0027] FIG. 11 is a conceptual rendering of an exposure apparatus
that uses the EUV light.
[0028] FIG. 12 is one example of a conventional measuring system of
an EUV light source.
[0029] FIG. 13 is an other example of a conventional measuring
system of an EUV light source.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] The First Embodiment
[0031] The instant embodiment explains a spectrum measuring
apparatus that can obtain a wavelength intensity distribution of
entire beams emitted from an EUV source and the measuring procedure
that uses it.
[0032] FIG. 1 is a schematic view of measuring a light intensity of
a laser plasma light source that is one method of EUV light source
by the spectrum measuring apparatus according to the present
invention.
[0033] In a measurement chamber 17 of the spectrum measuring
apparatus, an incident beam 18 from an EUV light source that passes
through an aperture 16 decreases in light intensity by an pinhole
array 1 where a lot of pinholes are located, and after passing a
filter 2 and filter 3 to select a wavelength of the measured beam,
is incident in a light intensity detector 4. The EUV light is
partially absorbed by a gas molecule that exists in the measurement
chamber 17, and attenuates. Therefore, it is desirable to exhaust
in the measurement chamber 17 to high vacuum to increase the
measurement accuracy.
[0034] The pinhole array 1 has a function to adjust the almost all
incidence beam in the measurement chamber 17 to suitable light
intensity for the measurement. FIG. 2 is shown that one example of
the pinhole array 1. The plural pinhole array 1 as shown in FIG. 2
are housed in the measurement chamber 17 selectable, and can
attenuate the incidence beam from the EUV light source to
predetermined ratio as for example 1/10, 1/100, 1/1000. Moreover,
it is also possible to pass the all intensity incidence beam
without attenuation. The pinhole array 1 is switched by moving the
pinhole array 1 by a motor 5. The attenuation factor with the
pinhole array 1 switches according to the maximum output of the
measured light source and kind of the light source (LPP method and
DPP method etc.), uses, and is adjusted to suitable light intensity
for the measurement by the measuring apparatus latter part.
[0035] FIG. 3 shows an example of an array pattern of the pinhole
array 1. FIG. 3A is a pattern of same diameter hole by the overall
even pitch, FIG. 3B is a random pattern, and FIG. 3C is a pattern
evenly arranged in a direction of the diameter in consideration of
the shape of the condenser mirror. The pattern of these pinhole
arrays are selected so that the light that passed the pinhole array
1 is not causing an unnecessary diffraction etc. and the beam never
locally concentrates on the filter 2 and 3, or the light intensity
detector 4. The numerical rate is selected so that it is adjusted
to suitable light intensity for the measurement by the measuring
apparatus latter part. FIG. 4 shows the state when the pinhole
array 1 is not used. When the beam from the EUV light source has a
low intensity, as shown in FIG. 4, it measures without attenuating
the beam by the pinhole array 1.
[0036] It is desirable to redirect the emitting light to the filter
2 and 3 or the detector 4 by considering the distance with the
pinhole array 1 and the filter 2 and 3 or a receiving inspection
plane of the pinhole array 1. It is desirable that the diameter of
the pinhole is larger than the measured wavelength because there is
maximum wavelength of light that cannot pass through the pinhole
array 1. Therefore, it is desirable to have the pinhole diameter
ten times larger or more than the wavelength.
[0037] For example, the detector 4 of the instant embodiment uses a
calorie meter that detects the light intensity as thermal energy.
When measuring the beam with a wavelength ?=10 .mu.m near the upper
bound of the detection wavelength of the calorie meter, if the
distance L with the receiving inspection plane of the detector 4 is
40 mm, the shade off amount on a focus plane (detection plate)
becomes 2.9 mm by using the pinhole array 1 (hole diameter
d=.phi.0.14 mm), and it is enough to prevent that the beam locally
concentrates on the light volume detector 4. The pinhole diameter
of .phi.0.14 mm does not interrupt the beam because the pinhole
diameter is sufficiently larger than the measured wavelength ?=10
.mu.m.
[0038] The filters 2 and 3 are used to combine one or two filters
if necessary, and to pass only the beam with the measured
wavelength band. It is effective to change a material and a
thickness etc. of the filter to select the wavelength band of the
passed beam. The material of the filter is selected from CaF.sub.2
(fluorite), MgF.sub.2 (magnesium fluoride), ZnSe (zinc selenide),
Si, Thallium-Bromide Chloride and optical glass that contain a
material that absorbs light below a specific wavelength region.
[0039] There is a mechanism to arrange the filters 2 and 3 in the
measurement chamber 17, and the filter that passes the desired
wavelength band to be measured and the state that the filter is not
used can be selected by the motor 5.
[0040] After attenuating by the pinhole array 1 and the specific
wavelength is cut out by the filter 2 and 3, the light intensity of
the incidence light are measured with the detector 4. FIG. 5 shows
the absorptance of each wavelength of the calorie meter used by the
instant embodiment. As shown in FIG. 5, the calorie meter can
absorb light with the absorptance of 90% or more in the wide
wavelength band, and measure the light intensity. A CCD and a
photodiode etc. can be used for others as the detector.
[0041] The cooling apparatus to keep below a predetermined
temperature is located in a part that light is irradiated from the
EUV light source such as the aperture 16, the pinhole array 1,
filter 2 and 3, the detector 4 mentioned above. A chamber inner
wall 19 is coated by a material that absorbs light easily to
suppress a diffuse reflection of the light (especially, infrared
light) that is reflected by the pinhole array 1. If a reflection
coefficient of the chamber inner wall is about 0.1 or less toward
the measured light with all wavelength bands, the measuring error
by the diffuse reflection is in an allowed range.
[0042] In FIG. 1, a structure of the EUV light that the spectrum is
measured by the spectrum measuring apparatus of the instant
embodiment according to the present invention is as follows.
However, the spectrum measuring apparatus according to the present
invention can be applied also to an EUV light source that has a
structure different from the EUV light source shown in FIG. 1.
[0043] In the EUV light source shown in FIG. 1, a nozzle 8 that
supplies a target 10 (for example, Xenon etc.) in an EUV light
source chamber 14 is located, and the target 10 is supplied. The
target 10 generates a plasma 7 with a pulse laser 13 that is
emitted from a laser generation apparatus 12 and condenses on the
target 10, and radiates the beam including the EUV light. The
radiated light includes, besides the EUV light used for the
exposure, the light of wavelength band in large range such as the
EUV light outside the band, X-ray, ultraviolet light, visible
light, infrared light. The majority of the target 10 used to
generate the plasma is collected by a target collection mechanism
9, and taken out outside of the chamber.
[0044] The EUV light with wavelength used for the exposure that is
radiated from the plasma 7 is condensed by a condenser mirror 11 of
spheroid to improve the use efficiency. The condenser mirror 11
generally uses the multilayer mirror that has a silicon layer and
molybdenum layer of a certain film thickness where the reflectivity
becomes the maximum for EUV light of wavelength used for projection
exposure are alternately formed by already-known method.
[0045] Therefore, the part of the light radiated from the plasma 7
is absorbed by the condenser mirror 11 composed of the
above-mentioned multilayer mirror without reflecting, and the light
measured by the spectrum measuring apparatus according to the
present invention is the light that is reflected by the condenser
mirror 11.
[0046] In the EUV light source shown in FIG. 1, the condenser
mirror 11 is composed of spheroid shape, makes the position in
which the plasma 7 is generated the other focus, and condenses the
reflection light in the condenser point 6. The spectrum measuring
apparatus according to the present invention can be applied also to
the EUV light source, for example, that radiate a parallel light
according to a structure different from the EUV light source shown
in FIG. 1.
[0047] The EUV light source chamber 14 is connected with the
measurement chamber 17 by a bellows 15. Moreover, the aperture 16
forms a transmission part near the condenser point 6. The aperture
16 is located for the purpose to reduce the inflow of the gas from
the EUV light source chamber 14 to the measurement chamber 17,
because of it is desirable that the EUV light source chamber 14 is
maintained about 10 Pa of pressure that is higher than the
measurement chamber 17 of the spectrum measuring apparatus to
reduce a pollution and a damage of the condenser mirror 11 by a
dispersion material from the plasma 7.
[0048] Thereinafter, a description will be given of spectrum
measuring method by the spectrum measuring apparatus shown in FIG.
1.
[0049] First, all light volume of light from the EUV light source
is measured. FIG. 4 shows the state of the spectrum measuring
apparatus when the all amount of the light from the EUV light
source is measured. To measure the all amount of the light from the
EUV light source, as shown in FIG. 4, when the pinhole array 1 and
the filter 2 and 3 are removed, detecting by the detector 4.
[0050] The detector 4 used by the instant embodiment is the calorie
meter, has detection sensitivity shown in FIG. 5. In other words,
the detector 4 has the sensitivity that can detect 95% or more in
the band of wavelength 100 nm or less, about 100% in the EUV light
with wavelength of 13.5 nm, 88% or more in the minimum part of the
long-wavelength band, and about 93% in the average. Moreover,
because the detector 4 has the sensitivity to wavelength of about
30 .mu.m on the long-wavelength band side, an all light volume Wt
that is almost all of the light radiated from the EUV light source
is detected by the calorie meter. An absolute light intensity is
obtained by correcting the detection result by using the
absorptance to the wavelength of the calorie meter shown in FIG.
5.
[0051] In the instant embodiment, the pinhole array 1 is removed
and the all light intensity Wt is measured. However, when the light
intensity from the EUV light source is large and exceeds a capacity
of the calorie meter, it may be measured by using the pinhole array
1 that has suitable attenuation factor.
[0052] Next, the pinhole array 1 is selected based on detected all
light intensity Wt. to attenuate the light intensity so that the
filter 2 and 3 used for later are not damaged. FIG. 6 shows the
state of the spectrum measuring apparatus when the pinhole array 1
that has an extinction rate of 1/100 is selected. It is desirable
to measure the light intensity from the EUV light source without
using the filter 2 and 3 to confirm the accurate attenuation factor
of the selected pinhole array 1 as shown in FIG. 6. When the light
intensity detected by the detector 4 via the pinhole array 1
decreases to the light intensity Wp1 by measuring, shown in FIG. 6,
the actual extinction rate of the pinhole array 1 can be obtained
by Wp1/Wt.
[0053] Next, the light intensity is measured in each frequency
band. FIG. 7 shows the state that the pinhole array 1 that has the
extinction rate of 1/100 and the one filter 2 that the absorption
edge is an already-known filter insert in an optical path to
measure the light intensity of the specific wavelength band. A
filter a that shuts out light with the wavelength region of 390 nm
or less is used as one example of the filter 2 in FIG. 7. FIG. 8
shows absorption characteristics of the filter a and the filter b.
The filter a has the transmittance only for the light with the
wavelength region of 390 nm or more as shown in FIG. 8. For
example, a general optical glass filter like the sharp cut filter
made by SHIGMA KOKI CO., LTD. can be used as the filter a and
filter b.
[0054] When irradiating the light from the EUV light source while
shown in FIG. 7, the light intensity Wf1' to which the wavelength
band that is attenuated by the pinhole array 1, and cut out by the
filter a is decreased. The light intensity Wf1' is the light
intensity in the wavelength region of 390 nm or more, the light
intensity Wf1 of light with the wavelength region with 390 nm or
more is obtained by considering the transmittance of the filter a
in the region and the sensitivity of the detector 4.
[0055] Next, in the filter a exchange with a filter b that shuts
out the light below the wavelength region of 560 nm, and the
similar measuring, a light intensity Wf2' is detected by the
detector 4. The light intensity Wf2' is the light intensity in the
wavelength region of 560 nm or more, the light intensity Wf2 of
light with the wavelength region with 560 nm or more is obtained by
considering the transmittance of the filter b in the region and the
sensitivity of the detector 4. Moreover, the subtraction of the
light intensity Wf1 and the light intensity Wf2 becomes the light
intensity Wf of 390 nm to 560 nm under the existence of the pinhole
array 1, and the absolute light intensity If1 of the wavelength
band of 390 nm to 560 nm that be reflected from the EUV light
source is obtained by considering the extinction rate F of the
pinhole array 1.
[0056] As an example of other materials used, as the filter 2, it
is possible to use the filters of ZnSe (zinc selenide) or Si
(silicon) of 5 mm thickness. In this case, ZnSe transmits the light
with wavelength of 0.6 .mu.m or more to 20 .mu.m, and Si transmits
the light with wavelength of 1.2 .mu.m or more to 15 .mu.m. The
light with wavelength of 15 to 20 .mu.m can not be substantially
detected by the detector 4 because of the almost same wavelength as
the wavelength radiated from a material at almost the room
temperature by the radiation. Thereby, the absolute light intensity
of light with wavelength of 0.6 .mu.m to 1.2 .mu.m is obtained by
using the above-mentioned filter.
[0057] As mentioned above, measuring the light intensity in each
part of the spectrum distribution of light from the EUV light
source becomes possible by switching to the filter that has the
absorption range in the measured wavelength band. As the result,
the spectrum distribution and absolute intensity of the entire
emitting light can be decided by considering these.
[0058] The Second Embodiment
[0059] FIG. 9 shows a spectrum measuring apparatus of the second
embodiment according to the present invention. FIG. 9 shows the
state to apply the spectrum measuring apparatus according to the
present invention to the discharge method plasma light source (DPP)
that is one method of EUV light source. The instant embodiment
chiefly explains a point different from the first embodiment.
[0060] The discharge method plasma light source (DPP) generates the
plasma by discharging the high density current pinch electrical
discharge etc., and takes out the EUV light. Because the DDP method
differs from the LLP method in construction, the condenser mirror
cannot be arranged on the upstream side of a discharge electrode 21
(the plasma emission point is base, the opposite side of the side
that the exposure apparatus and the measuring apparatus is
attached), a grazing incidence mirror 22 to condense the emitting
light from the electrical discharge electrode 21 to the downstream
side. Thereby, in the condenser point 6, there expects to be a
higher percentage of light elements present other than EUV light
elements compared to the LPP method.
[0061] Therefore, when the spectrum measuring apparatus according
to the present invention is applied to the EUV light source of the
DPP method, it is desirable to cover the chamber inner wall 19 with
the material that absorbs light easily to prevent the diffuse
reflection of the light that is reflected by the pinhole array 1.
Moreover, it is also desirable to arrange an antireflection board
23 that coats similar to the chamber inner wall 19 to increase an
area that absorbs the light. If the reflection coefficient is about
0.1 or less, these coatings do not harmfully influence the
measurement in the wavelength band of the measured light. However,
if the reflection coefficient is 0.05 or less, it is more
desirable.
[0062] Thereinafter, a description will be given of spectrum
measuring method by the spectrum measuring apparatus shown in FIG.
9. FIG. 10 shows one example of the transmittance distribution of
the spectrum filter that is used by the spectrum measuring
apparatus shown in FIG. 9.
[0063] For example, when the filter a and filter b are composed of
materials that have different absorption ranges, the spectrum
measuring apparatus shown in FIG. 9, to similar the first
embodiment, can measure the light intensity of a prescribed
wavelength region from the difference of the light intensity that
the detector 4 detects.
[0064] On the other hand, the instant embodiment explains the
method of measuring the light intensity of a prescribed wavelength
region by using the filter a and a filter c that are composed of
the same material, and only thickness is different.
[0065] Generally, the transmittance decreases in proportion to the
square of thickness when paying attention to the transmittance in
the specific wavelength range of the filter composed of a
homogeneous material. Therefore, for two different wavelengths,
their transmittances will change differently with different filter
thicknesses. Especially, in the vicinity of the absorption range of
the material that composes the filter, measuring the light
intensity of each detailed wavelength region becomes possible by
using this.
[0066] Concretely, the filter a shown in FIG. 10 has the
transmittance of about 90% in 450 nm or more, but the transmittance
decreases rapidly in 450 nm or less, becomes about 40% in 400 nm,
and becomes substantially opaque in vicinity of 380 nm. On the
other hand, when using the filter c that composed of the same
material as the filter a and has twice the thickness as filter a,
the transmittance of about 81% can be kept in 450 nm or more, and
it becomes the transmittance of about 16% in 400 nm. When the
thickness of the filter increases, using the phenomenon that the
transmittance decreases especially greatly for certain wavelength
can form the wavelength filter that has low transmittance. The
wavelength filter by such the technique is effective to the
wavelength region that the transmittance rapidly changes, and
changing the thickness of the filter one by one and measuring can
obtain a detailed spectrum.
[0067] As mentioned above, obtaining the absolute light intensity
in each wavelength region according to the difference of the
transmittance caused because the thickness of the filter that uses
the material corresponding to the measured wavelength band is
switched one by one becomes possible.
[0068] This application claims foreign priority benefits based on
Japanese Patent Applications No. 2003-299649, filed on Aug. 25,
2003, which is hereby incorporated by reference herein in its
entirety as if fully set forth herein.
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